Method of drying solid combustible material



T. RIGBY METHOD oF DRYING somn GOMBUSTIBLE MATERIAL Filed Aug. 22, 1921 Patented Dec. 2, 924.

UNITED STATES THOMAS BIGBY, or L01\TDON,E1\TGLAND.

METHOD OF DRYING SOLID COMBUSTIBLE MATERIAL.

Application filed August 22, '1921. Serial No. 494,264.

(GRANTED UNDER THE PROVISIONS OF THE ACT MARCH 3, 1921, 41 STAT. 12., 1313.)

f0 all whom it may concern:

, Be it known that I, THOMAS RIGBY, subject of the Kin of England, residing at London, Englan have invented certain new and useful Improvements in Methods of Drying Solid Combustible Material (for which I have filed application in Great Britain, No. 18,920, filed 20th August, 1913, accepted 20th August, 1914, patent sealed 5th November, 1924; and in Germany, No. 324,07 9, filed 25th October, 1913), of which the following is a specification.

This invention relates to the drying of solid combustible material (and especially of fuels such as peat or lignite) as by suspending the same in a comminuted condition in a current of hot gases such as combustion gases.

In drying such material by suspending it in a current of hot gases, I have observed that variability in the temperature of the gases, of the water content of the raw material, etc., are so liable to u set the balance in any predetermined set 0 drying conditions, and to result on the one hand in ir regularly dried material, or on the'other hand, in unnecessary loss of heat, and generally speaking in inefficiency, that despite various proposals for attaining a predetermined result by choice of appropriate length of the drying duct and use of heat-storage elements or to control the drying by regulation ofthe gas speed or temperature (ineluding addition of hot gases from an auxiliary source or addition of cooled exit gases) andof the feed of moist material, such variability still markedly influences the results.

According to the present invention, however, I provide a method of practically overcoming these remaining difficulties, which is based upon certain observations made by me. I have ascertained that the harmful variations above referred to are most markedly reflected in variation of temperature of the gases at the end of the drying operation, and that if the latter temperature be maintained between the limits of 75 C. and 150 C. imperfect and uneconomical working is avoided.

One featuer of the present invention consists, therefore, in maintaining the temperature of the outflowing gases between these limits, and while this can be effected in a variety of ways having regard to the differout controllable elements above referred to p which play a part in this stage of the process and including the state of division of the raw material, the control is most conveniently effected by varying the rate of introduction of the moist material into the gas current, or by bye-passing some of the gas, or adding to the gas stream cooled gases which have already done their work.

Figures 1 and 2 indicate diagrammatically a lignite fuel briquetting plant,-in which the method according to the invention may be put into practice.

In these drawings, which will be used in explaining an example of the invention in which the regulation of the outlet temperature is effected by variation of the lignite feed, arepresents a distintegrator, which reduces the lignite to a fine powder, which is then passed to a bunker b. The bucket wheel a, driven by variable gear 0! then takes the material and introduces it into an upright duct 6, projecting it into the main drying duct The resistance to gas flow in the duct e, on account of the appropriately se-- leeted length and diameter, is such that the amount of air entering with the powder does not appreciably increase the percentage of oxygen in the drying gases from the boiler or other furnace p. t h is a 31 which causes the necessary gas flow through the duct; while i represents a battery of cyclone dust separators, discharging into the lignite bunker j, situated over the briquetting press k. The chimney Z constitutes the gas outlet, and is provided with washers m for catching last traces of dust. The whole of the duct, as well as its auxiliaries, is constructed of such strength that in the unlikely event of an explosion, the system itself escapes damage, and the excess pressure is rapidly dissipated from the chimney Z.

To deal with ,any local fires of deposited powder which may succeed such an explosion, nozzles n, n are provided, which may be opened upon the occurrence of an undue rise of temperature to admit water or steam, although the extinction of a fire may be equally effected by the introduction of an excess of the wet l gnite. In normal working, it is desirable, before a temporary shutdown, to introduce steam into the duct when the feed of raw material is cut ofl, so that a cushion of steam is interposed between the last dried portions, and any air which may enter the duct inadvertently in place of the flue gases.

The regulation of the drying is in this case effected by varying the rate of revolution of the feed wheel 0 to maintain the temperature at 0 (at the cyclone outlet) within the limits desired.

The following are examples of drying conditions which experience has shown appropriate in one particular case Percentage of water in the lignite, by weight.

Percentage of water in the dried lignite, 12% by weight.

Average size of particles of the powdered lignite, 1' millimetre.

Average temperature of the flue gases at point of entry of the material, 250 centigrade.

Length of duct between lignite entry and outlet, 40 metres.

Diameter of duct, 190 centimetres.

Velocity of gas current, 15 metres per second.

Approximate time of contact of the powder and the hot gases, 2.6 seconds.

By the method according to the present invention, it will be understood, the whole of the lignite can be dried down to briquetting condition, or it may only be partly dried, the remainder of the water being ex elled in the customary manner. On the other hand, aportion only of the material to be briquetted may be fully dried in the improved way, and the remainder, where for example requirements of form or of size in the dry product impose special conditions, may be wholly or partly dealt with in Schulze or other driers, and their separate products afterwards reunited for brhvqietting.

hat I claim as my invention and desire to secure by Letters Patent is z N 1. The method of drying solid combustible material which comprises dispersing the material in a comminuted condition in a current of hot gas, causing thematerial to be deposited from the gas current after a period of suspension therein sufiicient to effect the desired degree of dryin and maintainin during the drying, a su stantially stea y tem erature of the gas at the point where the ried material is deposited ing the moist material in a pulverized cona current of hot gas, causing the material from the current by variation of the rate of dispersal. of the material into the current in the comminuted condition aforesaid.

2. The method of drying solid fuel such as peat or lignite which comprises conveying the same in and by a hot gas current which carries away the moisture, withdrawing the dried material from this gaseous current and limiting the temperature of the gas in contact with the dried material at the conclusion of the conveying aforesaid to between about and C.

3. The method of continuously drying lignite which consists in continuously dispersdition in a current of hot combustion gases, maintaining it in suspension in and by said current until dried to the desired extent, continuously depositing the product from the gas current and regulating one or more of the variables, such as the rate of feed of the moist material, in accordance with the temperature of the current where the dried material leaves it to maintain this temperature between about 75 and 150 C.

4. The method of drying solid combustible material which comprises dispersing the material in a comminuted condition in ries away the moisture, withdrawing the dried material from this gaseous current and limiting the temperature of the gas in contact with the dried material at the conclusion of the conveying aforesaid to between about 75 and 150 C.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

THOMAS RIGBY.

Witnesses:

J. D. Bonn. F. H. Yomw 

